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                    <div id="mw-content-text" lang="en" dir="ltr" class="mw-content-ltr"><div class="t-navbar" style=""><div class="t-navbar-sep"> </div><div class="t-navbar-head"><a href="../c.html" title="c"> C</a><div class="t-navbar-menu"><div><div><table class="t-nv-begin" cellpadding="0" style="line-height:1.1em;">
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<p><b>ISO/IEC 9899:2011</b>, a.k.a. <b>C11</b>, is a previous revision of the C standard.
</p>
<h2><span class="mw-headline" id="Obsolete">Obsolete</span></h2>
<h3><span class="mw-headline" id="Removed">Removed</span></h3>
<ul><li> <span class="t-lc"><a href="io/gets.html" title="c/io/gets">gets()</a></span>
</li></ul>
<h2><span class="mw-headline" id="New_language_features">New language features</span></h2>
<ul><li> Multithreaded environments
<ul><li> <a href="language/atomic.html" title="c/language/atomic">Atomic objects</a> (<a href="keyword/_Atomic.html" title="c/keyword/ Atomic"><tt>_Atomic</tt></a>)
</li><li> <a href="language/storage_duration.html#Storage_duration" title="c/language/storage duration">Thread local storage</a> (<a href="keyword/_Thread_local.html" title="c/keyword/ Thread local"><tt>_Thread_local</tt></a>)
</li></ul>
</li><li> Enhanced alignment support
<ul><li> <a href="language/_Alignof.html" title="c/language/ Alignof">Alignment query</a> (<a href="keyword/_Alignof.html" title="c/keyword/ Alignof"><tt>_Alignof</tt></a>)
</li><li> <a href="language/_Alignas.html" title="c/language/ Alignas">Alignment strengthening</a> (<a href="keyword/_Alignas.html" title="c/keyword/ Alignas"><tt>_Alignas</tt></a>)
</li><li> Over-aligned types
</li></ul>
</li><li> Unicode support
<ul><li> <a href="language/character_constant.html" title="c/language/character constant"><code>u</code>/<code>U</code> character constants</a>
</li><li> <a href="language/string_literal.html" title="c/language/string literal"><code>u8</code>/<code>u</code>/<code>U</code> string literals</a>
</li></ul>
</li><li> <a href="language/generic.html" title="c/language/generic">Generic selection expressions</a> (<a href="keyword/_Generic.html" title="c/keyword/ Generic"><tt>_Generic</tt></a>)
</li><li> <a href="language/_Noreturn.html" title="c/language/ Noreturn">Non-returning functions</a> (<a href="keyword/_Noreturn.html" title="c/keyword/ Noreturn"><tt>_Noreturn</tt></a>)
</li><li> Anonymous <a href="language/struct.html" title="c/language/struct">struct</a> and <a href="language/union.html" title="c/language/union">union</a> members
</li><li> Fine-grained <a href="language/eval_order.html" title="c/language/eval order">evaluation order</a>
</li><li> Extending the lifetime of <a href="language/lifetime.html#Temporary_lifetime" title="c/language/lifetime">temporary objects</a>
</li><li> <a href="language/static_assert.html" title="c/language/ Static assert"><tt>_Static_assert</tt></a>
</li><li> <a href="language/analyzability.html" title="c/language/analyzability">Analyzability</a>
</li></ul>
<h3><span class="mw-headline" id="Feature_test_macros_for_optional_features">Feature test macros for optional features</span></h3>
<ul><li> <a href="preprocessor/replace.html" title="c/preprocessor/replace"><tt>__STDC_ANALYZABLE__</tt></a>
<ul><li> Indicates analyzability is supported.
</li></ul>
</li><li> <a href="preprocessor/replace.html" title="c/preprocessor/replace"><tt>__STDC_LIB_EXT1__</tt></a>
<ul><li> Indicates bounds checking functions are supported.
</li></ul>
</li><li> <a href="preprocessor/replace.html" title="c/preprocessor/replace"><tt>__STDC_NO_ATOMICS__</tt></a>
<ul><li> Indicates atomic objects and the atomic operation library are not supported.
</li></ul>
</li><li> <a href="preprocessor/replace.html" title="c/preprocessor/replace"><tt>__STDC_NO_COMPLEX__</tt></a>
<ul><li> Indicates complex types and the complex math functions are not supported.
</li></ul>
<dl><dd> These features were mandatory in C99.
</dd></dl>
</li><li> <a href="preprocessor/replace.html" title="c/preprocessor/replace"><tt>__STDC_NO_THREADS__</tt></a>
<ul><li> Indicates thread local storage and the thread support library are not supported.
</li></ul>
</li><li> <a href="preprocessor/replace.html" title="c/preprocessor/replace"><tt>__STDC_NO_VLA__</tt></a>
<ul><li> Indicates <a href="language/array.html#Variable-length_arrays" title="c/language/array">variable length arrays and variably modified types</a> are not supported.
</li></ul>
<dl><dd> These features were mandatory in C99.
</dd></dl>
</li></ul>
<h2><span class="mw-headline" id="New_library_features">New library features</span></h2>
<h3><span class="mw-headline" id="New_headers">New headers</span></h3>
<ul><li> <code>&lt;stdalign.h&gt;</code>
</li><li> <code>&lt;stdatomic.h&gt;</code>
</li><li> <code>&lt;stdnoreturn.h&gt;</code>
</li><li> <code>&lt;threads.h&gt;</code>
</li><li> <code>&lt;uchar.h&gt;</code>
</li></ul>
<h3><span class="mw-headline" id="Library_features">Library features</span></h3>
<ul><li> <a href="thread.html" title="c/thread">Concurrency support library</a>
</li><li> <a href="memory/aligned_alloc.html" title="c/memory/aligned alloc"><tt>aligned_alloc()</tt></a>
</li><li> UTF-16/32 type aliases
<ul><li> <a href="string/multibyte/char16_t.html" title="c/string/multibyte/char16 t"><tt>char16_t</tt></a>
</li><li> <a href="string/multibyte/char32_t.html" title="c/string/multibyte/char32 t"><tt>char32_t</tt></a>
</li></ul>
</li><li> UTF-16/32 conversion functions
<ul><li> <span class="t-lc"><a href="string/multibyte/mbrtoc16.html" title="c/string/multibyte/mbrtoc16">mbrtoc16()</a></span>
</li><li> <span class="t-lc"><a href="string/multibyte/mbrtoc32.html" title="c/string/multibyte/mbrtoc32">mbrtoc32()</a></span>
</li><li> <span class="t-lc"><a href="string/multibyte/c16rtomb.html" title="c/string/multibyte/c16rtomb">c16rtomb()</a></span>
</li><li> <span class="t-lc"><a href="string/multibyte/c32rtomb.html" title="c/string/multibyte/c32rtomb">c32rtomb()</a></span>
</li></ul>
</li><li> <span class="t-lc"><a href="program/quick_exit.html" title="c/program/quick exit">quick_exit</a></span>
</li><li> <span class="t-lc"><a href="program/at_quick_exit.html" title="c/program/at quick exit">at_quick_exit</a></span>
</li><li> Exclusive modes of <span class="t-lc"><a href="io/fopen.html" title="c/io/fopen">fopen()</a></span> and <span class="t-lc"><a href="io/freopen.html" title="c/io/freopen">freopen()</a></span> (<span class="t-c"><span class="mw-geshi c source-c"><span class="st0">"x"</span></span></span>)
</li><li> <a href="error.html#Bounds_checking" title="c/error">Bounds checking functions</a>
</li><li> <a href="chrono/timespec.html" title="c/chrono/timespec"><tt>timespec</tt></a>
</li><li> <a href="chrono/timespec_get.html" title="c/chrono/timespec get"><tt>timespec_get()</tt></a>
</li><li> <a href="numeric/complex/CMPLX.html" title="c/numeric/complex/CMPLX"><tt>CMPLX(F|L)?</tt></a>
</li><li> New numeric limit macros
<ul><li> <a href="types/limits.html" title="c/types/limits"><tt>(FLT|DBL|LDBL)_DECIMAL_DIG</tt></a>
</li><li> <a href="types/limits.html" title="c/types/limits"><tt>(FLT|DBL|LDBL)_TRUE_MIN</tt></a>
</li><li> <a href="types/limits.html" title="c/types/limits"><tt>(FLT|DBL|LDBL)_HAS_SUBNORM</tt></a>
</li></ul>
</li><li> Thread local <span class="t-lc"><a href="error/errno.html" title="c/error/errno">errno</a></span>
</li></ul>
<h2><span class="mw-headline" id="Defect_reports">Defect reports</span></h2>
<p><a href="https://en.cppreference.com/mwiki/index.php?title=Template:c/language/history/DR11&amp;action=edit&amp;redlink=1" class="new" title="Template:c/language/history/DR11 (page does not exist)">Template:c/language/history/DR11</a>
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<h2><span class="mw-headline" id="Compiler_support">Compiler support</span></h2>
<p><a href="https://en.cppreference.com/mwiki/index.php?title=Template:c/compiler_support/11&amp;action=edit&amp;redlink=1" class="new" title="Template:c/compiler support/11 (page does not exist)">Template:c/compiler support/11</a>
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